How about an interactive crash course where they have to write down 3 words. Then 3 weeks later they have to enter the 3 words to unlock a prize. It could be a free course worth $150 sponsored by a hardware wallet or just some sats.

2 of 3 Multisig would be great so they could be guided through the steps over a period of time.

Also you could charge a fee for holdings over a certain amount so that people are pushed to withdraw.

"they dont know what keys are" They don't have to know that, they just have to know that the 12 words are the password to their bitcoin. It is super important to provide backup instruction to prevent scams. On top of the list should be a link and a warning "read these instructions before entering your 12 words" and then a questionaire as "you could be victim of a scam" "who told you to enter your words" etc

"they don't understand why to take custody" they probably also don't want to take custody :D Probably this is the hardest part. How can you convince someone to do something hard when there is an easy and convenient alternative? Maybe an interplay of pointing our dangers "your money is at risk, backup now" followed with positive benefits could work.

"They dont udnerstand how valuable bitcoin will be one day" Maybe analogies like one bitcoin one house and some math would help

"they wont read article or watch video, they assume wallet is as secure as Bitcoin itself" The reality is that most people will prefer a bank or service to hold their keys. Just like the majority of people trust the government and inject any "medicine" without asking questions. There is no way to change that, sorry, you can just stay humble and educate.